1. Field of the Invention
The present invention relates to a zoom lens, an image sensing optical device and a digital appliance. For example, the present invention relates to: a zoom lens that is optimum for, among image sensing optical systems having a zoom function, an image sensing optical system whose angle of view at a wide-angle end exceeds 100°; an image sensing optical device that outputs, as an electrical signal, a picture of a subject taken in with the zoom lens and an image sensing element; and a digital appliance having an image input function, such as a digital camera, that incorporates such an image sensing optical device.
2. Description of Related Art
Conventionally, as a zoom lens suitable for an image sensing optical system, the following zoom lenses are proposed.
Patent document 1: Japanese Unexamined Patent Application Publication No. 2009-271165
Patent document 2: Japanese Unexamined Patent Application Publication No. 2012-108279
In general, since in a zoom lens whose angle of view at a wide-angle end exceeds 100°, the position of an on-axis marginal light ray that passes through a first group is lowered at a wide-angle end, when the zoom ratio of the lens is increased, variations in longitudinal chromatic aberration caused by zooming tend to be increased. Although in order to reduce variations in longitudinal chromatic aberration, it is effective to use an achromatic lens within the first group, this increases the number of lenses having a large diameter, with the result that the cost and the size of the lens system are increased.
In the zoom lens disclosed in patent document 1, in order to correct a longitudinal chromatic aberration, an achromatic lens is used within a first group. However, since the achromatic lens is not located in a position effective for correcting the longitudinal chromatic aberration because it is required to reduce the size, it is impossible to obtain an effect of sufficiently correcting the chromatic aberration. In the zoom lens disclosed in patent document 2, an achromatic lens is located in a position advantageous for correcting a longitudinal chromatic aberration. However, since the entire length of a first group is long, the diameter of the lens that is the closest to an object side with respect to the angle of view is increased, with the result that the size of the lens system is increased.